1. Technical Field
The present invention relates to a thermal printing device having a head element, and relates more particularly to a printing device capable of accurately determining the state of deterioration of the head element while suppressing the amount of stored data.
The present invention also relates to a thermal printing device having a head element, and relates more particularly to a printing device capable of surveying the state of deterioration of the head elements in stages without interfering with the printing process, and suppressing the size of the circuitry.
The invention also relates to a printing device that detects deterioration of the printhead, and more particularly is capable of shortening the detection time while suppressing detection errors.
2. Related Art
Thermal printers are commonly used for printing sales receipts, for example. Such thermal printers have multiple head elements in the printhead, and print by applying voltage to the head elements and causing the resistive elements (heat elements) of the head elements to produce heat. If some of the head elements deteriorate, the print quality of such printers drops undesirably.
JP-A-2000-141730 teaches a method of detecting problems in the thermal head, and makes a good/no-good decision about the printhead based on the maximum and minimum resistance of the heat elements.
JP-A-H10-166637 discloses a method of detecting deterioration of the head elements while printing as an example of technology that increases the speed of detection.
JP-A-2011-148232 discloses a mechanism for checking operation of the head elements, capable of detecting defective (problem) elements in the thermal head of a thermal printer without applying heat to the head elements.
However, the method described in JP-A-2000-141730 detects whether head elements are good or no-good, and cannot assess change (advancement) in the deterioration of head elements.
Avoiding printing problems such as streaking of barcodes printed on receipts is essential in receipt printers used in retail stores, for example, and replacing head elements at an appropriate time before the head elements fail is desirable. More specifically, technology enabling more precisely managing deterioration of head elements is desirable.
It is also desirable to suppress the amount of data the printer must store in order to evaluate deterioration of the head elements.
Depending on the method used, checking for deterioration of the head elements of receipt printers used at the checkout counter in food service businesses and convenience stores that are open 24 hours a day may require stopping printing receipts, and this may interfere with business operations.
To address this problem, JP-A-H10-166637 teaches a method of providing a current detection resistor to every signal line and inspecting the head elements while printing receipts, but this method requires large-scale circuitry, resulting in a high cost.
Because the voltage application circuit described in JP-A-2011-148232 uses diodes as a reverse current protection circuit of the deterioration detection circuit, variation in the forward voltage can result in detection errors.
A FET (field effect transistor) may conceivably be used in the reverse current protection circuit to overcome this problem. However, if a smoothing capacitor is provided in the path of the printing current to suppress noise in such a voltage application circuit, the charge that is left from deterioration detection must be discharged, and such discharge is time-consuming.
There is also a danger with such voltage application circuits that the printing voltage may be applied to the small-signal control circuit unit of the detection circuit, and the small-signal control circuit may be destroyed by the application of such an over-voltage.
An objective of at least one embodiment of the invention is to provide a thermal printing device with head elements where the printing device is capable of accurately determining the state of deterioration of the head elements, and minimizing the amount of stored data.
Another objective of at least one embodiment of the invention is to provide a thermal printing device with head elements where the printing device is capable of surveying the state of deterioration of the head elements in stages without interfering with the printing process, and suppressing the size of the circuitry.
The invention also relates to a printing device that detects deterioration of the printhead, and more particularly is capable of shortening the detection time while suppressing detection errors.
Another objective of the invention is to provide a printing device that can reliably prevent damage to the detection circuit resulting from application of an over-voltage.